Method of detecting an abrupt variation in an electrical alternating quantity

Abstract

A method of detecting an abrupt variation in a periodic electrical quantity, where a criterion for the occurrence of the abrupt variation is formed from samples of the periodic quantity. To be able to carry out such a method in such a way that the abrupt variations in the periodic quantity can be detected with a high sensitivity, the periodic quantity is weighted in an FIR filter with a transfer function with a double zero position at the nominal frequency; the output signal of the FIR filter is monitored for whether it reaches a threshold indicating that an abrupt variation in the periodic quantity has occurred.

What is claimed is:  
     
       1. A method of detecting an abrupt variation in a periodic electrical quantity of an electric power system having a nominal frequency, comprising the steps of: 
       applying the periodic electrical quantity to an FIR filter;  
       weighting the periodic electrical quantity in the FIR filter with a transfer function to generate an output signal, the transfer function having a value of zero at a double zero position at the nominal frequency of the electrical power system; and  
       monitoring the output signal of the FIR filter to determine if the output signal reaches a threshold value, the threshold value indicating an occurrence of the abrupt variation in the periodic electrical quantity.  
     
     
       2. The method according to  claim 1 , wherein the transfer function also has an additional zero position at a zero frequency. 
     
     
       3. A circuit arrangement for detecting an abrupt variation in a periodic electrical quantity of an electrical power system having a nominal frequency, comprising: 
       an FIR filter having an input and an output, the FIR filter having a transfer function with a value of zero as a double zero at a position of the nominal frequency of the electrical power system, the input of the FIR filter receiving the periodic electrical quantity, and  
       a comparator coupled to the output of the FIR filter and generating an output signal, the output signal indicating the abrupt variation when the output of the FIR filter reaches a threshold value.